A cash dispenser is an electro-mechanical apparatus that is used inside a cash machine to dispense paper money upon request. A cash dispenser normally consists of a control logic board, a communication port to host machine, a motorized transfer mechanism, for example, motors, belts, rollers, and pulleys, and an array of multiple cash cassettes.
U.S. Pat. No. 6,903,358 discloses using a very small analog signal achieved from using a light sensor. However, the movement of the slit to shade the light amount falling on the sensor is very small. Thus, the voltage changes from the sensor requires large amplification and yields low SNR.
A Rotary Variable Differential Transformer (RVDT) may be used for angular detection of the idler deflection angle. The mechanical arms and links to turn the RVDT is subject to slop. The finite mass of the mechanical arms and links add significant inertia to the motion causing a delay in initial movement and an overshoot at peak angle. The pendulum effect of the mass gives a ringing (decaying oscillation) signal. RVDT is easily affected by a nearby magnetic field (for example, the driving motor or solenoid). The signal output is an AC signal that requires complex and fast circuit for momentary signal capture.
A cash dispenser has a mechanical system to remove a single piece of banknote one at a time from a stack inside the cash cassette, usually by frictional rollers and pressure plates. However if this mechanical system fails due to different humidity levels, or mechanical aging (for example, the material of the rollers become old and stiff), two or more banknotes are likely to be removed at the same time. It is desirable to provide an apparatus to detect if this situation occurs to improve reliability of the cash dispenser. Therefore a new detection method is important for all paper-like media handling machines.